1. Field of the Invention
The invention generally relates to a pad structure, and more particularly, to a pad structure used in a circuit carrier or an integrated circuit chip for connecting a conductive ball or a conductive bump.
2. Description of Related Art
In the electronic industry, soldering is a major connecting technology, for example, used for flip chip bonding between a chip and a carrier or connection between a common electronic part and a circuit board. For bonding process, in addition to solder, pad itself and pad surface material, a pad structure plays a critical role to affect bonding reliability.
The multiple functions and miniature of a chip have become a tendency of electronic products, which accordingly requires an increased density of contacts. Under the above-mentioned situation, for some signals with a specific electrical requirement (for example, low impedance, high frequency, coupling sensitivity and the like), the line width and line of the chip need to be increased, which results in a space limitation.
The outer diameter of a pad depends on the and the dimension of soldering balls or bumps and the dimension of solder mask openings. In other words, the outer diameter of a pad greatly depends on the pad structure and thereby determines the distance between two adjacent pads or the layout space of the trace lines, which however is not advantageous for the flexibility of layout design.
When the layout space of the trace lines is not enough, the layout space of the trace lines can be increased by reducing line width and line interval, but it would degrade the electrical performance, for example, causing signal reflection, crosstalk and coupling. Along with the tendency of high density of contacts, the above-mentioned problem becomes more and more serious.